Electro-hydraulic control system diagnostics

ABSTRACT

Various embodiments of methods, apparatus and systems that diagnose and/or detect faults of an electro-hydraulic control system for a transmission are presented. Some embodiments, adjust a main line pressure of the electro-hydraulic control system and detect faults based upon changes in a pressure switch resulting from such adjustments of the main line pressure. The pressure switch may be incorporated into a control main valve or a clutch trim valve of the electro-hydraulic control system.

TECHNICAL FIELD

The present invention relates generally to electro-hydraulic controlsystems for transmissions, and more particularly to diagnostics for anelectro-hydraulic control system of a transmission.

BACKGROUND

In general, an automatic transmission of a motor vehicle includes anumber of selectively engageable friction elements (referred to hereinas clutches). Selective engagement/disengagement of the clutchesestablish speed ratios between the transmission input shaft and thetransmission output shaft. In particular, shifting from a currentlyestablished speed ratio to a new speed ratio generally involvesdisengaging a clutch (off-going clutch) associated with the currentspeed ratio and engaging a clutch (on-coming clutch) associated with thenew speed ratio.

The torque capacity of a clutch (on-coming or off-going) involved in ashift is controlled by the fluid pressure that a clutch trim valvesupplies to the clutch. The clutch trim valve receives a main line fluidpressure and supplies the clutch with a clutch feed pressure developedfrom the main line fluid pressure. In a typical system, an electroniccontrol module (ECM) provides a solenoid valve of the clutch trim valvewith a control signal. The control signal controls a pilot pressure ofthe solenoid valve which in turn controls the clutch feed pressuresupplied to the clutch.

In such systems, the operation of one component generally depends uponthe operation of other components. Accordingly, when troubles arise,identifying the faulty component or components is a difficult task andcommonly requires a substantial amount of trial and error. As can beappreciated, such diagnostic techniques are time consuming and costly.

SUMMARY

According to one aspect of disclosed embodiments, a method for detectingfaults in an electro-hydraulic control system for a transmissionincludes initiating a delivery of fluid to the electro-hydraulic controlsystem. The method also include adjusting regulator control signals thatrequest a main regulator valve of the electro-hydraulic control systemto develop a main line pressure, and receiving status signals thatindicate status of a pressure switch of the electro-hydraulic controlsystem, status of the pressure switch being based upon the main linepressure. The method also includes detecting faults based upon regulatorcontrol signals and status signals indicative of status of the pressureswitch, and generating one or more diagnostic signals that areindicative of detected faults.

According to some aspects, the method may detect a fault of the pressureswitch in response to the status signals indicating the pressure switchis in an active state prior to initiating the delivery of fluid. Themethod may also cease the delivery of fluid to the electro-hydrauliccontrol system, and detect a fault of the pressure switch in response tothe status signals indicating the pressure switch is in an active stateafter ceasing the delivery of fluid.

In other aspects, adjusting regulator control signals may includegenerating regulator control signals that request the main regulatorvalve to increase the main line pressure from a nominal level to a firstpressure level, and detecting faults may include detecting a fault ofthe electro-hydraulic control system in response to status signalsindicating the pressure switch is in an inactive state and regulatorcontrol signals requested the main regulator valve to increase the mainline pressure to the first pressure level. Adjusting regulator controlsignals may further include generating regulator control signals thatrequest the main regulator valve to increase the main line pressure fromthe first pressure level to a second pressure level, and detectingfaults may further include detecting a fault of the electro-hydrauliccontrol system in response to status signals indicating the pressureswitch is in an active state and regulator control signals requested themain regulator valve to increase the main line pressure to the secondpressure level. Adjusting regulator control signals may also includegenerating regulator control signals that request the main regulatorvalve to reduce the main line pressure from the second pressure level toa third pressure level, and detecting faults may include detecting afault of the electro-hydraulic control system in response to statussignals indicating the pressure switch is in an inactive state andregulator control signals requested the main regulator valve to decreasethe main line pressure to the third pressure level.

In another aspect, detecting faults may include detecting, based uponthe regulator control signals and the status signals that indicatestatus of the pressure switch, that the pressure switch has failed to anopen state, and generating one or more diagnostic signals may includegenerating one or more diagnostic signals that indicate the pressureswitch has failed to the open state. Detecting faults may includedetecting, based upon the regulator control signals and the statussignals that indicate status of the pressure switch, that the pressureswitch has failed to a closed state, and generating one or morediagnostic signals may include generating one or more diagnostic signalsthat indicate the pressure switch failed to the closed state. Detectingfaults may further include detecting, based upon the regulator controlsignals and the status signals that indicate status of the pressureswitch, that a fluid supply source failed to deliver fluid to theelectro-hydraulic control system, and generating one or more diagnosticsignals may also include generating one or more diagnostic signals thatindicate the fluid supply source failed to deliver fluid to theelectro-hydraulic control system.

In another aspect, detecting faults may include detecting, based uponthe regulator control signals and the status signals that indicatestatus of the pressure switch, that the electro-hydraulic control systemfailed to increase the main line pressure above a threshold pressurelevel associated with the pressure switch, and generating one or morediagnostic signals may includes generating one or more diagnosticsignals that indicate the electro-hydraulic control system failed toincrease the main line pressure above the threshold pressure level.Detecting faults may also include detecting fluid leakage based upon theregulator control signals and the status signals that indicate status ofthe pressure switch, and generating one or more diagnostic signals mayinclude generating one or more diagnostic signals that indicate fluidleakage detected. Detecting faults may also include detecting, basedupon the regulator control signals and the status signals that indicatestatus of the pressure switch, that the electro-hydraulic control systemfailed to decrease the main line pressure below a threshold pressurelevel associated with the pressure switch, and generating one or morediagnostic signals may include generating one or more diagnostic signalsthat indicate the electro-hydraulic control system failed to decreasethe main line pressure below the threshold pressure level.

In yet another aspect, an electro-hydraulic control system for atransmission includes a pressure switch, a plurality of valves, and anelectronic control module. The pressure switch receives fluid, opens inresponse to a pressure level of the fluid being greater than a thresholdpressure level, closes in response to the pressure of the fluid beingless than the threshold pressure level, and generates a status signalthat indicates status of the pressure switch. The plurality of valvesdevelop a main line pressure based upon regulator control signals,develop a control main pressure based upon the main line pressure, anddevelop a clutch feed pressure based upon clutch control signals, themain line pressure, and the control main pressure. The plurality ofvalves further selectively deliver fluid at the control main pressure tothe pressure switch based upon a pressure level of the main linepressure. The electronic control module generates regulator controlsignals to control the main line pressure, generates clutch controlsignals to control the clutch feed pressure, and detects faults basedupon regulator control signals and status signals of the pressureswitch.

In some aspects, the plurality of valves includes a control main valveto develop the control main pressure. The control main valve includes aport to receive the main line pressure, and a port to supply fluid atthe control main pressure in response to receiving the main linepressure. The control main valve further includes the pressure switchand a valve member that selectively directs the control main pressure tothe pressure switch based upon a pressure level of the main linepressure.

In other aspect, the plurality of valves includes a clutch trim valve todevelop the clutch feed pressure based upon clutch control signals, themain line pressure, and the control main pressure. The clutch trim valveincludes a port to receive the main line pressure, and a port to receivethe control main pressure, and a port to supply the clutch feedpressure. The control main valve further includes the pressure switchand a valve member that selectively directs the control main pressure tothe pressure switch based upon a pressure level of the main linepressure.

In some aspects, the electronic control module adjusts regulator controlsignal to increase the main line pressure from a nominal level to afirst pressure level, and detects a fault in response to status signalsindicating the pressure switch is open and regulator control signalsrequested the main line pressure be increased to the first pressurelevel. The electronic control module may further adjust regulatorcontrol signals to increase the main line pressure from the firstpressure level to a second pressure level, and may detect a fault inresponse to status signals indicating the pressure switch is closed andregulator control signals requested the main line pressure be increasedto the second pressure level. The electronic control module may furtheradjust regulator control signals to reduce the main line pressure fromthe second pressure level to a third pressure level, and may detect afault in response to status signals indicating the pressure switch isopen and regulator control signals requested the main line pressure bedecreased to the third pressure level.

In some aspects, the electronic control module may detect based upon theregulator control signals and the status signals that a fluid supplysource failed to deliver fluid. The electronic control module may alsodetect fluid leakage based upon the regulator control signals and thestatus signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments described herein are illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements.Furthermore, some reference labels may include a superscript and/orsubscript to identify a particular item of a group of corresponding oranalogous items; but such superscripts and/or subscripts may be omittedto refer to the group of items or a non-specific item of the group.

FIG. 1 shows an embodiment of a vehicle having a power train and aelectro-hydraulic control system to selectively engage clutches of thepower train.

FIG. 2 shows an embodiment of a main regulator valve of theelectro-hydraulic control system of FIG. 1.

FIG. 3 shows an embodiment of a control main valve of theelectro-hydraulic control system of FIG. 1 in a regulating position.

FIG. 4 shows an embodiment of a clutch trim valve of theelectro-hydraulic control system of FIG. 1 in a regulating position.

FIG. 5 shows a flowchart for an embodiment of a diagnostic method forthe electro-hydraulic control system of FIG. 1.

FIG. 6 shows a graph of main line pressure in response to the diagnosticmethod of FIG. 5.

DETAILED DESCRIPTION

Aspects of specific embodiments are presented by way of example in thedrawings and described in detail. However, such aspects are susceptibleto various modifications and alternative forms. Accordingly, theparticular forms disclosed are not intended to be limiting, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the appended claims.

Specific details regarding aspects of illustrative embodiments are setforth in order to provide a more thorough understanding. However, someembodiments may practice such aspects without such specific details. Inother instances, certain aspects have not been shown in detail in ordernot to obscure other aspects of the illustrative embodiments.

References in the specification to “one embodiment”, “an embodiment”,“an illustrative embodiment”, etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic; however, other embodiments may not necessarily includethe particular feature, structure, or characteristic. Moreover, suchphrases are not necessarily referring to the same embodiment. When aparticular feature, structure, or characteristic is described inconnection with an embodiment, other illustrative embodiments may alsoinclude such a particular feature, structure, or characteristic whetheror not explicitly described.

Embodiments may be implemented in hardware, firmware, software, or anycombination thereof. Embodiments may also be implemented as instructionsstored on a machine-readable medium, which may be read and executed byone or more processors. A machine-readable medium may include anymechanism for storing information in a form readable by a machine (e.g.,a computing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; and others.

Details of the present invention may be described herein with referenceto either normally high solenoids or normally low solenoids. A normallyhigh solenoid develops or permits a high output pressure in response toreceiving no electrical control signal or an electrical control signalhaving a low duty cycle. A normally high solenoid conversely develops alower output pressure or prevents development of a high output pressurein response to receiving an electrical control signal or an electricalcontrol signal with a high duty cycle. In contrast, a normally lowsolenoid develops or permits a high output pressure in response toreceiving an electrical control signal or an electrical control signalwith a high duty cycle. A normally low solenoid further develops a loweroutput pressure or prevents development of a high output pressure inresponse to receiving no electrical control signal or an electricalcontrol signal having a low duty cycle. The following illustratedembodiments use normally low solenoids. However, one of ordinary skillin the art may readily replace one or more of the normally low solenoidsof the illustrated embodiments with normally high solenoids and modifyother aspects of the illustrated embodiments to account for thereplacement.

Referring now to FIG. 1, a power train 10 of a vehicle is shown. Thepower train 10 includes an engine 20, a torque converter 30, atransmission 40, a final drive assembly 50, an electro-hydraulic controlsystem 60, and a fluid supply system 80. The engine 20 may include aspark-ignited engine, a diesel engine, an electric hybrid engine (e.g. acombustion engine powering an electric generator that powers an electricengine), or the like. As shown, an output 22 of the engine 20 may becoupled to the torque converter 30, and the torque converter 30 may becoupled to an input shaft 42 of the transmission 40. The torqueconverter 30 generally receives torque from the engine output 22 andfluidically transfers the received torque to the transmission inputshaft 42, thus permitting the rotation of the engine output 22 to differfrom the rotation of the transmission input shaft 42. In someembodiments, the torque converter 30 may mechanically lock the engineoutput 22 to the transmission input shaft 42 once the input shaft 42achieves a rotation rate similar to the rotation rate of the engineoutput 22.

As further shown, an output shaft 44 of the transmission 40 is coupledto the final drive assembly 50 that provides the vehicle withlocomotion. The final drive assembly 50 may include wheels, continuoustracks, turbines, and/or other drive equipment. Further, the final driveassembly 50 may further include a transfer case to selectively delivertorque received via the transmission output shaft 44 to such wheels,continuous tracks, and/or other engine driven equipment. For example,the transfer case may selectively transfer torque to front wheels, backwheels, or all wheels of the vehicle.

The transmission 40 also includes gearsets 46 and clutches 48. Thegearsets 46 and clutches 48 cooperate to provide a plurality ofselectable speed ratios and output ranges between the input shaft 42 andthe output shaft 44. For example, the gearsets 46 and clutches 48 mayprovide neutral ratios, multiple reverse speed ratios, and/or multipleforward speed ratios. In one embodiment, the transmission 40 includesthree interconnected planetary gearsets 46 and five clutches 48 that arecontrollable to provide six forward speed ratios or “gears”. Otherconfigurations of gearsets 46 and clutches 48 are also possible.

The electro-hydraulic control system 60 controls operation of thetransmission 40 and in particular the selected speed ratio between theinput shaft 42 and the output shaft 44. As shown, the control system 60includes a range selector 64, a main regulator valve 66, a control mainvalve 68, and several clutch trim valves 70. The control system 60further includes an electronic control module (ECM) 72 to control andmonitor the fluid supply system 80, the range selector 64, the mainregulator valve 66, the control main valve 68, and the clutch trimvalves 70.

The fluid supply system 80 is fluidically coupled to torque converter30, the main regulator valve 66, the control main valve 68, and theclutch trim valves 70 via main lines or conduits 74. Further, thecontrol main valve 68 is coupled to the clutch trim valves 70 viacontrol lines or conduits 76.

The fluid supply system 80 includes a sump 82 coupled to various exhaustlines or conduits 78 in order to receive fluid collected from componentsof the power train 10 such as torque converter 30, transmission 40,clutches 48, and valves 66, 68, 70. The fluid supply system 80 includesan engine driven pump 84 coupled to main lines 74 to pump fluid from thesump 82 to components of the power train 10 such as the torque converter30, transmission 40, clutches 48 and valves 66, 68, 70. As discussed inmore detail below, the main regulator valve 66 and the clutch trimvalves 70 are controlled by solenoids, such as variable bleed solenoids,on/off solenoids, or similar devices that regulate fluid pressuredeveloped by the main regulator valve 66 and clutch trim valves 70.

As mentioned above, the ECM 72 controls and monitors various componentsof the power train 10. To this end, the ECM 72 is coupled to componentsof the power train 10 via one more links 90 such as wires, CAN networksand the like. Only a few illustrative links 90 are shown in FIG. 1 so asnot to obscure other aspects of the illustrative embodiment. Via links90, the ECM 72 provides components of the power train 10 with controlsignals to control their operation and may receive data or statussignals from components of the power train 10 that provide informationregarding their operation. For example, the ECM 72 may control operationof the transmission 40 based on status signals received from the engine20, the torque converter 30, the transmission 40, the range selector 64,and/or other components. Such status signals may include electricaland/or analog signals received from sensors, controls or other likedevices associated with the vehicle components. For instance, statussignals may include signals indicative of transmission input speed,driver requested torque, engine output torque, engine speed, temperatureof the hydraulic fluid, transmission output speed, turbine speed, brakeposition, gear ratio, torque converter slip, and/or other measurableparameters.

The ECM 72 may include computer circuitry such as one or moremicroprocessors and related elements configured to process executableinstructions expressed in computer programming code or logic stored inone or more tangible computer readable media. The ECM 72 may alsoinclude analog to digital converters and/or other signal processingcircuitry or devices to process one or more of the status signalsreceived from the vehicle components. While shown in FIG. 1 as a singleblock, ECM 72 may be implemented as separate logical and/or physicalstructures. For example, the ECM 72 may be physically and/or logicallyseparated from electronic controls for the transmission 40 or electroniccontrols for the engine 20. All or portions of the ECM 72 mayalternatively or in addition be executed by a controller that is noton-board the vehicle, such as an external controller located at atransmission manufacturer or an assembly location.

As mentioned above the valves 66, 68, 70 regulate fluid pressuresupplied to various components of the power train 10. In particular, themain regulator valve 66 generates an adjustable main line pressure MP,and the control main valve 68 develops a control main pressure CP inresponse to receiving fluid at the main line pressure MP. Moreover, eachclutch trim valve 70 generates a clutch feed pressure CF for arespective clutch 48 based upon clutch control signals, the main linepressure MP, and the control main pressure CP.

The main regulator valve 66 may support a range (e.g. about 50-about 300psi) of main line pressures MP. The ECM 72 may generate regulatorcontrol signals that cause the main regulator valve 66 to adjust themain line pressure MP to a desired main line pressure (e.g. about 200psi). The main line pressure MP developed by the main regulator valve 66is routed to various components via main lines 74 and may be used tohydraulically actuate components such as clutches 48. The control mainvalve 68 develops and supplies an intermediate control main pressure CP(e.g. about 50-about 100 psi) in response to receiving the main linepressure MP. Control lines 76 may provide fluid at the control mainpressure CP to control various components of the electro-hydrauliccontrol system 60. In particular, solenoids of the main regulator valve66 and clutch trim valves 70 may receive fluid at the control mainpressure CP and such solenoids may use the control main pressure CP toadjust the pressures developed by the main regulator valve 66 and clutchtrim valves 70. Each clutch trim valve 70 may support a range of clutchfeed pressures CF (e.g. about 0-about 300 psi). The ECM 72 may generateclutch control signals that cause each clutch trim valve 70 to adjustits clutch feed pressure CF to a desired clutch feed pressure CF. Byvarying the clutch control signals, the ECM 72 may fully engage,disengage and/or partially engage/disengage a clutch 48 of thetransmission 40.

As mentioned above, the ECM 72 controls operation of the main regulatorvalve 66 via regulator control signals. In particular, the ECM 72generates regulator control signals based upon shift requests,transmission temperature, solenoid specifications, and potentially otherparameters. The relationship between regulator control signals and mainline pressure MP is generally initially set according to specificationsprovided by the supplier or manufacturer of the main regulator valve 66.In particular, supplier specifications typically provide P/I curves,charts, or tables that relate the main line pressure MP developed by themain regulator valve 66 to the regulator control signals received by themain regulator valve 66. Thus, based upon such P/I curves, charts, ortables, the ECM 72 may generate regulator control signals to develop themain line pressure MP at a desired pressure level.

The ECM 72 may modulate or adjust the pressure level of the main linepressure MP for various reasons. For example, the ECM 72 may modulatethe main line pressure MP to increase fluid flow through a cooler (notshown) during idle. The ECM 72 may also modulate the main line pressureMP to increase fuel economy of the vehicle. For example, the ECM 72 maylower the main line pressure MP to a level just above what is requiredto maintain clutch capacity in order to reduce fuel consumption.

Referring now to FIG. 2, further details regarding one embodiment of themain regulator valve 66 are presented. As shown, the main regulatorvalve 66 includes a pressure regulator valve 220, a solenoid valve 230and an accumulator 240. The pressure regulator valve 220 includes avalve body 200 having a solenoid port 210, an overage port 212, a mainline port 214, and a feedback port 216. The solenoid port 210 is coupledto the solenoid valve 230 and to the accumulator 240 via a restrictor222. The overage port 212 may be coupled to exhaust lines 78 to returnoverage or fluid exhausted from the main regulator valve 66 to the sump82 of the fluid supply system 80. The main line port 214 may be coupledto the fluid supply system 80 via main line 74. Likewise, the feedbackport 216 may be coupled to the fluid supply system 80 via main line 74and restrictor 224.

The valve body 200 further includes an axial valve bore 250 thatfluidically couples the ports 210, 212, 214, and 216. The pressureregulator valve 220 further includes a valve member 260 positioned inaxial bore 250 of the valve body 200. The valve member 260 includes anupper land 262 and a lower land 264 that effectively divide the valvebore 250 into an upper chamber 270 between the upper land 262 and anupper end 202 of the valve body 200, a middle chamber 272 between thelands 262, 264, and a lower chamber 274 between the lower land 264 and alower end 204 of the valve body 200.

The valve member 260 is slideably moveable along the axial valve bore250. In particular, a spring 280 positioned in the lower chamber 274between the lower end 204 of the valve body 200 and the lower land 264biases the valve member 260 toward the upper end 202 of the valve body200 until a seat 266 of the valve member 260 rests against the upper end202 of the valve body 200. A solenoid pressure supplied to the lowerchamber 274 by the solenoid valve 230 biases the valve member 260 towardthe upper end 202. Conversely, main line pressure MP supplied to theupper chamber 270 via feedback port 216 biases the valve member 260toward the lower end 204 of the valve body 200. Thus, the valve member260 moves toward the upper end 202 if the spring 280 and solenoid valve230 exert a greater force upon the valve member 260 than the forceexerted upon the valve member 260 by the main line pressure MP.Conversely, the valve member 260 moves toward the lower end 204 if thespring 280 and solenoid valve 230 exert a lesser force upon the valvemember 260 than the force exerted upon the valve member 260 by the mainline pressure MP.

As shown in FIG. 2, when the valve member 260 is positioned toward theupper end 202, the land 264 decouples the overage port 212 from themiddle chamber 272. In such a position, the main line pressure MPcreated by the fluid supply system 80 is applied to the land 262 via themiddle chamber 272. However, when the valve member 260 is moved towardthe lower end 204, the land 264 moves past the overage port 212 thusventing the middle chamber 272 to the exhaust lines 78. Venting themiddle chamber 272 to the exhaust lines 78 reduces the pressure in themiddle chamber 272 and therefore reduces the main line pressure MPapplied to the land 262. Venting of the middle chamber 272 occurswhenever the main line pressure is sufficient to overcome the biasingforces of spring 280 and the solenoid output pressure of valve 230.Accordingly, by controlling the fluid pressure in the lower chamber 274,the ECM 72 may regulate the main line pressure MP. To this end, the ECM72 in one embodiment provides the solenoid valve 230 with regulatorcontrol signals that result in the solenoid valve 230 modulating thesolenoid output pressure applied to the lower chamber 274 and therebyadjusting the position of the valve member 260 in the bore 250. Thus,the ECM 72 may modulate the main line pressure MP by causing thesolenoid valve 230 to selectively connect the main line port 214 to theexhaust line 78.

As explained in more detail below, the ECM 72 implements a diagnosticmethod that detects certain faults in the electro-hydraulic controlsystem 60 based upon status signals of a pressure switch. In oneembodiment, the pressure switch is incorporated into the control mainvalve 66. In another embodiment, the pressure switch is incorporatedinto one of the clutch trim valves 70. Thus, it is envisioned that someembodiments of the electro-hydraulic control system 60 may include aconventional control main valve 68 without a pressure switch, aplurality of conventional clutch trim valves 70 without a pressureswitch, and a clutch trim valve 70 with a pressure switch. It is furtherenvisioned that some embodiments of the electro-hydraulic control system60 may include the control main valve 68 with a pressure switch and aplurality of conventional clutch trim valves 70 without pressureswitches. It is further envisioned that the electro-hydraulic controlsystem 60 may include more than a single pressure switch in order topermit further diagnostics of the electro-hydraulic control system 60.

Referring now to FIG. 3, a control main valve 68 with a pressure switch350 is shown that is suitable for the diagnostic method presented belowin regard to FIG. 5. The control main valve 68 includes a valve body 300having a feedback port 310, an upper control port 312, and a lowercontrol port 314. The valve body 300 includes an upper exhaust port 320,a middle exhaust port 322, and a lower exhaust port 324. The valve body300 further includes a main port 330 and a switch port 332. In oneembodiment, a control line 76 of the electro-hydraulic control system 60is coupled to the feedback port 310 via a restrictor 313. The controlline 76 is also coupled to the upper control port 312 and the lowercontrol port 314 of the valve body 300. The main line 74 is coupled tothe main port 330, and the exhaust lines 78 are coupled to the exhaustports 320, 322, 324.

The valve body 300 further includes an axial valve bore 350 thatlongitudinally traverses the valve body 300. The valve bore 350fluidically couples the ports 310, 312, 314, 320, 322, 324, 330 and 332.The control main valve 68 further includes a valve member 360 positionedin axial bore 350 of the valve body 300. The valve member 360 includesan upper land 362, a middle land 364, and a lower land 366 thateffectively divide the valve bore 350 into an upper chamber 370 betweenthe upper land 362 and an upper end 302 of the valve body 300, an uppermiddle chamber 372 between the upper land 362 and the middle land 364, alower middle chamber 374 between the middle land 364 and the lower land366, and a lower chamber 376 between the lower land 366 and a lower end304 of the valve body 300. Further, the valve member 360 is slideablymoveable along the axial valve bore 350. In particular, a spring 380positioned in the lower chamber 376 between the lower end 304 of thevalve body 300 and the lower land 366 biases the valve member 360 towardthe upper end 302 of the valve body 300 until a seat 368 of the valvemember 360 rests against the upper end 302 of the valve body 300.

The control main valve 68 has a non-regulating state (not shown), wherethe valve member 360 is fully stroked, i.e., positioned in the bore 350such that the stem 369 of the valve member 360 rests against the lowerend 304 of the body 300. FIG. 4 depicts the control main valve 68 inanother non-regulating state where the valve member 360 is fullystroked, i.e., positioned in the bone 350 such that the seat 368 restsagain the upper end 302 of the valve body 300. The control main valve 68also has a regulating state as depicted in FIG. 3, in which the valvemember 360 is positioned in the bore 350 such that the valve member 360does not rest against either the upper end 302 or the lower end 304 ofthe body 300. Thus, in one embodiment, the control main valve 68 has aregulating state and two non-regulating states (e.g. a stroked state anda de-stroked state).

The control main valve 68 develops a control main pressure CP at apressure level that is dependent upon the main line pressure MP suppliedto the main line port 330. When no fluid is supplied to the control mainpressure CP via the main line port 330, the spring 380 biases the valvemember 360 toward the upper end 302, thus placing the control main valve68 in the de-stroked non-regulating state. In the de-stroked state, thevalve member 360 fluidically couples the main line 74 to the controlline 76 via the upper middle chamber 372 while blocking the exhaustports 320, 322. Accordingly, as fluid is introduced to the upper middlechamber 372 via the main line port 330, the valve member 360 directs thefluid to the upper control port 312 which further directs fluid to thepressure switch 350 via the lower control port 314 and the lower middlechamber 374. Pressurization of the pressure switch 350 changes the stateof pressure switch 350, and may result in either issuance of ortermination of an electrical signal by pressure switch 350 to ECM 72,depending upon the configuration of the switch.

As the main line pressure MP is increased, fluid is introduced to theupper chamber 370 via the upper middle chamber 372 and the ports 310,312. The increased fluid pressure in the upper chamber 370 applies adownward force upon the valve member 360. Eventually, the pressure inthe upper chamber 370 exerts a downward force upon the valve member 360that is greater than the upward force of the spring 380. As a result ofsuch force, the valve member 360 moves toward the lower end 304 of thevalve body 300. As shown in FIG. 3, downward movement of the valvemember 360 eventually decouples the main line port 330 from the uppermiddle chamber 372. Continual downward movement of the valve member 360further couples the upper middle chamber 372 to exhaust port 320, thusexhausting fluid from the upper middle chamber 372 and reducing thefluid pressure in the upper middle chamber. Similarly, such downwardmovement of the valve member 360 further couples the lower middlechamber 374 to exhaust port 322, thus exhausting fluid from the lowermiddle chamber 372 and the pressure switch 350 and reducing the fluidpressure in the lower middle chamber 374. When the pressure switch 350is fully exhausted, it changes states again. The change in state ofpressure switch 350 results in either issuance of or termination of anelectrical signal by pressure switch 350 to ECM 72.

As a result of the above arrangement of ports, valve member 360 andspring 380, the control main valve maintains or regulates the controlmain pressure CP at a substantially constant pressure level once themain line pressure MP is greater than a threshold pressure level (e.g.100 psi). Above such threshold pressure level, the main line pressure MPplaces the control main valve 68 in the regulating state. In theregulating state, the valve member 360 vents the lower middle chamber374 to the exhaust lines 78, thus venting fluid from the middle chamber374 and the pressure switch 350. Further, the valve member 360selectively vents the upper middle chamber 372 to the exhaust lines 78to maintain the control main pressure CP at a predetermined pressurelevel (e.g. 100 psi). As the main line pressure increases, the controlmain valve 68 vents the upper middle chambers 372 to the exhaust lines78 more frequently and as the main line pressure decreases, the controlmain valve 68 vents the middle chambers 372, 374 to the exhaust lines 78less frequently.

As the main line pressure MP is decreased below the threshold pressurelevel, the valve member 360 moves toward the upper end 302, thus causingthe lower middle chamber 374 and therefore the pressure switch 350 toreceive fluid via the control port 314. The pressure switch 350 in oneembodiment is designed to open in response to receiving fluid above apredefined pressure level and to close in response to the received fluiddropping below the predefined pressure level. However, it should beappreciated that the pressure switch 350 may alternatively be designedto close in response to receiving fluid above the predefined pressurelevel and to open in response to the received fluid dropping below thepredefined pressure level. Moreover, the pressure switch 350 is designedto generate a status signal that indicates the state of the pressureswitch 350 (e.g. opened or closed; activated or deactivated). Thus, dueto the configuration of the control main valve 68 the status of thepressure switch 350 is dependent upon whether the control main valve 68is in a regulating state or a non-regulating state. Accordingly, thestatus signal produced by the pressure switch 350 is indicative ofwhether the control main valve 68 is in a regulating state or anon-regulating state.

Referring now to FIG. 4, a clutch trim valve 70 with a pressure switch450 is shown that is suitable for the diagnostic method described belowin regard to FIG. 5. As shown, the clutch trim valve 70 is part of theclutch control valve assembly 70 of the electro-hydraulic control system60. The clutch trim valve 70 includes a pressure regulator valve 420, asolenoid valve 430 and an accumulator 490. The pressure regulator valve420 includes a valve body 400 having a solenoid port 410, a control port412, exhaust ports 424, 426, a main port 431, a switch port 432, aclutch feed port 434, and a clutch feedback port 436. The solenoid port410 is in fluid communication with the solenoid valve 430. The solenoidport 410 is also in fluid communication with the accumulator 490 via anaccumulator port 438 and a restrictor 492. A control passage 76 iscoupled to an upper middle chamber 472 of the pressure regulator valve420 via the control port 412. Exhaust passages 77, 78 are coupled to theexhaust ports 424, 426, respectively. A main passage 74 is coupled tothe main port 431, and a clutch passage 79 is coupled to a lower middlechamber 474 of the pressure regulator valve 420 via the clutch feed port434. The clutch passage 79 is further coupled to a lower chamber 476 ofthe pressure regulator valve 420 via the clutch feedback port 436 and arestrictor 496.

The pressure regulator valve 420 has a valve member 460 that is axiallytranslatable in a valve bore 450 of the valve body 400. The ports 410,412, 414, 422, 424, 426, 430, 432, 434, 436, and 438 are in fluidcommunication with the valve bore 450. The valve member 460 includes anupper land 462, a middle land 464, and a lower land 466 that effectivelydivide the valve bore 450 into an upper chamber 470 between the upperland 462 and an upper end 402 of the valve bore 450, an upper middlechamber 472 between the upper land 462 and middle land 464, a lowermiddle chamber 474 between the middle land 464 and the lower land 466,and a lower chamber 476 between the lower land 466 and a lower end 404of the valve bore 450.

A spring 480 is positioned in the lower chamber 476 between the lowerend 404 of the valve bore 450 and the lower land 466. The spring 480biases the valve member 460 toward the upper end 402 of the valve bore450 until a seat 468 of the valve member 460 rests against the upper end402 of the valve body 400. A clutch control pressure supplied to theupper chamber 470 by the solenoid valve 430 biases the valve member 260toward the lower end 404. Conversely, main line pressure MP supplied tothe lower middle chamber 474 via main line port 431 biases the valvemember 460 toward the upper end 402 of the valve bore 450. Thus, thevalve member 460 moves toward the upper end 402 if the spring 480 andfluid pressure in the main passage 74 exert a greater force upon thevalve member 460 than the force exerted upon the valve member 460 by theclutch control pressure. Conversely, the valve member 260 moves towardthe lower end 404 if the spring 480 and fluid pressure in the mainpassage 74 exert a lesser force upon the valve member 460 than the forceexerted upon the valve member 460 by the clutch control pressure.

When the valve member 460 is destroked, i.e., positioned toward theupper end 402, the lower land 466 decouples the main port 431 from thelower middle chamber 474. The position of middle land 464 couples theexhaust port 426 to the lower middle chamber 474. In such a position,the valve member 460 vents the clutch passage 79 to the exhaust passage78 via the lower middle chamber 474, thus reducing the fluid pressure inthe lower middle chamber 474 and the clutch feed pressure CF in theclutch passage 79.

When the valve member 460 is stroked, i.e., moved toward the lower end404, the position of the middle land 464 decouples the lower middlechamber 474 from the exhaust port 424 and the position of the lower land466 exposes the lower middle chamber 474 to the main port 431, thusraising the pressure level of the lower middle chamber 474 and theclutch feed pressure CF in the clutch passage 79. Accordingly, bycontrolling the position of the valve member 460 of the clutch trimvalve 70, the ECM 72 may regulate or otherwise control the clutch feedpressure CF developed by the clutch trim valve 70. To this end, the ECM72 in one embodiment provides the solenoid valve 430 with clutch controlsignals that result in the solenoid valve 430 modulating the clutchcontrol pressure applied to the upper chamber 470 and thereby adjustingthe position of the valve member 460 in the bore 450. Thus, the ECM 72may modulate the clutch feed pressure CF by causing the solenoid valve430 to selectively exhaust the lower middle chamber 474 to the exhaustline 78. FIG. 4 shows the clutch trim valve 70 in such a modulating orregulating state.

In summary, the clutch trim valve 70 may be in a de-stroked state wherethe valve member 460 is positioned in the bore 450 such that the seat468 rests against the upper end 402 of the valve body 400. The clutchtrim valve 70 may conversely be in a stroked state where the valvemember 460 is positioned in the bore 450 such that the stem 469 of thevalve member 460 rests against the lower end 404 of the valve body 400.The clutch trim valve 70 may further be placed into a regulating stateas depicted in FIG. 4 in which the valve member 460 is positioned in thebore 450 such that no portion of the valve member 460 rests againsteither the upper end 402 or the lower end 404 of the body 400. Thus, inone embodiment, the clutch trim valve 70 has a regulating state and twonon-regulating states (e.g. a stroked non-regulating state and ade-stroked non-regulating state).

When the valve 420 is fully stroked, the control passage 76 is coupledto the upper middle chamber 472 and thereby pressurizes the pressureswitch 450. Thus, fully stroking of the valve 420 causes the pressureswitch 450 to change state (i.e., to either issue or cease issuing anelectrical signal to the ECM 72, depending on the configuration of theswitch).

Assuming a constant main line pressure MP, as the solenoid valve 430increases the clutch control pressure applied to the upper chamber 470,the increased fluid pressure in the upper chamber 470 applies a downwardforce upon the valve member 460. Eventually, the pressure in the upperchamber 470 exerts a downward force upon the valve member 460 that isgreater than the upward force of the spring 480. As a result of suchforce, the valve member 460 moves toward the lower end 404 of the valvebody 400. Downward movement of the valve member 460 eventually decouplesthe clutch 79 from the exhaust passage 426, and decouples the pressureswitch 450 from the exhaust passage 424. As a result, control pressureflows from control passage 76 to pressure switch passage 432, causingthe pressure switch 450 to change state as described above. Downwardmovement of the valve member 460 decouples the lower middle chamber 474from the exhaust port 426 and couples the lower middle chamber 474 tothe main line 74, thus increasing the pressure level in the lower middlechamber 474 and allowing main pressure to flow into the clutch feedpassage 434.

The increased pressure in the lower middle chamber 474 provides anupward force upon the valve member 460. Such increased pressure causesthe valve member 460 to translate upward thereby venting the lowermiddle chamber 474 to the exhaust passage 78 via port 426. As a resultof the above arrangement of ports, valve member 460 and spring 480, theclutch control valve 70 maintains or regulates the clutch feed pressureCF at a substantially constant pressure level for a given clutch controlsignal when the main line pressure MP is greater than a thresholdpressure level (e.g. about 130 psi). Above such threshold pressurelevel, the main line pressure MP places the clutch trim valve 70 in theregulating state shown in FIG. 4.

When the pressure regulator valve 420 transitions from the fully strokednon-regulating states to the regulating state, the land 464 decouplesthe upper middle chamber 472 from the control passage 76, therebydepressurizing the pressure switch 450. As a result, the pressure switch450 changes state (i.e., it either begins issuing or ceases issuing anelectrical signal to the ECM 72, depending on the configuration of theswitch). Thus, the pressure switch 450 changes state each time the valve420 changes from the regulating state to a fully stroked non-regulatingstate or vice versa.

While in the regulating state, the valve member 460 dithers, therebyselectively venting the lower middle chamber 474 to the exhaust line 78to maintain the clutch feed pressure CF at a predetermined pressurelevel (e.g. about 130 psi). As the main line pressure increases, theclutch trim valve 70 vents the lower middle chamber 474 to the exhaustline 78 more frequently and as the main line pressure MP decreases, theclutch trim valve 70 vents the lower middle chamber 474 to the exhaustline 78 less frequently.

Referring now to FIGS. 5 and 6, an embodiment of a diagnostic methodsuitable for detecting certain faults of the electro-hydraulic system 60is presented. At block 500, the ECM 72 initializes various components ofthe power train 10. In an embodiment where a pressure switch is coupledto a clutch trim valve 70, the ECM 72 verifies that the pressure switchis working properly as part of the initialization. More particularly,the ECM 72 expects the pressure switch to be in a particular electricalstate at initialization, i.e., prior to starting operation of the driveunit (e.g., the engine). Prior to engine startup, no fluid is flowingthrough the electro-hydraulic system 60. Therefore, if the pressureswitch on the trim valve 70 is not in the particular electrical stateexpected by the ECM 72 prior to engine start-up, the ECM determines thatthe pressure switch is not working properly (i.e., it is a faultypressure switch or has simply failed). The ECM 72 responds to such afailure condition in a normally expected manner. The particularelectrical state expected by the ECM 72 depends on the configuration ofthe pressure switch, i.e., the ECM 72 will expect either issuance orlack of issuance of an electrical signal from the pressure switch,depending upon configuration of the switch. The ECM 72 may generateclutch control signals that open the solenoid valve 430 and thus definea threshold pressure level between a regulating and a non-regulatingstate of the clutch trim valve 70. In one embodiment, the ECM 72performs the initialization process 500 in response to a key beingplaced in an ignition of the vehicle; however, other events such asturning the ignition, pressing a button, opening a door, etc. may alsoor alternatively trigger initialization process 500.

At block 505, the ECM 72 determines whether the pressure switch (e.g.350, 450) is active or inactive (e.g. open or closed) based upon thepresence or absence of electrical status signals received from thepressure switch. In one embodiment, the pressure switch is implementedsuch the pressure switch is closed when not receiving fluid above anactivating pressure level. However, it should be appreciated that thepressure switch (e.g. 350, 450) may be implemented so that it closeswhen activated by fluid above the activating pressure level.

At block 505, the ECM 72 determines whether the pressure switch respondscorrectly to the lack of application of fluid pressure. In theillustrated embodiment, the pressure switch is expected by ECM 72 to be“inactive” (e.g. closed) in the absence of fluid pressure and “active”(e.g. open) in the presence of fluid pressure above the threshold level.Accordingly, if the ECM 72 determines that the pressure switch is activewhen there is no fluid pressure, the ECM 72 at block 510 may determinethat the pressure switch has failed to an active state (e.g. failedopen).

If the status signal indicates the pressure switch is inactive in theabsence of fluid pressure, the ECM 72 at block 515 sets the main linepressure to a first pressure level PL1 and initiates at block 520delivery of fluid from the fluid supply system 80 to theelectro-hydraulic control system 60. In one embodiment, the ECM 72 atblock 515 generates regulator control signals that request the mainregulator valve 66 to increase the main line pressure MP to a firstpressure level PL1 that is less than a threshold pressure level TH ofthe valve with the pressure switch (e.g. control main valve 68 or theclutch trim valve 70). Moreover, the ECM 72 at block 515 generatesregulator control signals that request the first pressure level PL1 besufficient to fill the electro-hydraulic control system 60 with fluid.Thus, due to setting the first pressure level PL1 in this manner, theECM 72 ensures that fluid is delivered to components of theelectro-hydraulic control system 60 and especially to the pressureswitch while also ensuring that the valve with the pressure switchremains in a non-regulating state.

As noted above, the pump 84 of the fluid supply system 80 is driven bythe vehicle drive unit (e.g., an engine). Accordingly, in theillustrated embodiment, the ECM 72 and/or other controller of thevehicle at block 520 generates control signals that cause the fluidsupply system 80 to deliver fluid to the electro-hydraulic controlsystem 60 in response to cranking and/or igniting the engine 20. Inparticular, the ECM 72 and/or another controller of the vehicle maygenerate control signals that crank and ignite the engine 20 in responseto a user turning an ignition key. Thus, upon igniting the engine 20,the pump 84 delivers fluid to the main regulator valve 66. The mainregulator valve 66 in turn delivers fluid to main lines 74 and increasesthe main line pressure MP from a nominal pressure level to the firstpressure level PL1 (e.g. about 50 psi) specified by regulator controlsignals received from the ECM 72.

At block 525, the ECM 72 determines based upon status signals from thepressure switch whether the pressure switch changed states at a firstdiagnostic point DP1. See, FIG. 6. In particular, the ECM 72 in oneembodiment determines at block 525 whether the pressure switchtransitioned from the inactive state (e.g. closed state) to the activestate (e.g. open state).

In an embodiment where the pressure switch is incorporated into thecontrol main valve 68, the control main valve 68 remains in a de-strokedstate at block 525, due to the main line pressure MP being at the firstpressure level PL below the threshold pressure level TH for the controlmain valve 68. Accordingly, assuming normal operation, the main line 74delivers fluid to the pressure switch via ports 312, 314 and chambers372, 374. Thus, if the ECM 72 determines at block 525 that the pressureswitch 350 does not enter its active state (e.g. open state), then theECM 72 detects a fault in the electro-hydraulic control system 60 atblock 530 and may provide signals and/or other indicators of suchdetected fault. In particular, the ECM 72 may indicate that the pressureswitch 350 has failed to the inactive state (e.g. failed closed) and/orthat fluid was not delivered to the electro-hydraulic control system 60.For example, the pump 84 may not be primed, thus preventing delivery offluid to the electro-hydraulic control system 60.

Similarly, in an embodiment where the pressure switch is incorporatedinto a clutch trim valve 70, the clutch trim valve 70 fully strokes atblock 525, due to the main line pressure MP being at the first pressurelevel PL below the threshold pressure level TH for the clutch trim valve70. Accordingly, assuming normal operation, the control line 76 deliversfluid to the pressure switch 450 via ports 412, 414, 432 via uppermiddle chamber 472. Thus, if the ECM 72 determines at block 525 that thepressure switch 450 does not enter its active state (e.g. open state),then the ECM 72 detects a fault in the electro-hydraulic control system60 at block 530 and may provide signals and/or other indicators of suchdetected fault.

In response to determining that the pressure switch has transitionedfrom the inactive state (e.g. closed) to the active state (open) at afirst diagnostic point DP1, the ECM 72 at block 535 generates regulatorcontrol signals that request the main regulator valve 66 to increase themain line pressure MP to a second pressure level PL2 (e.g. 200 psi). Asa result of increasing the main line pressure MP above the thresholdpressure level TH for the valve with the pressure switch, the valveshould transition from a non-regulating state to a regulating state,thus causing its pressure switch to transition from an active state(e.g. open) to an inactive state (e.g. closed). In particular as shownin FIG. 3, the valve member 360 of the control main valve 66 decouplesthe control line 76 from the pressure switch 350 in the regulatingstate. Likewise, as shown in FIG. 4, the valve member 460 of the clutchtrim valve 70 decouples the control line 76 from the pressure switch 450in the regulating state.

Thus, the ECM 72 at block 540 determines whether the pressure switchchanged states at a second diagnostic point DP2. In particular, the ECM72 in one embodiment at block 540 determines based upon the statussignal of the pressure switch whether the pressure switch transitionedfrom an active state (e.g. open) to an inactive state (e.g. closed). Ifthe ECM 72 determines that the pressure switch did not change state atthe second diagnostic point DP2, then the ECM 72 detects a fault in theelectro-hydraulic control system 60 at block 545 and may provide signalsand/or other indicators of such detected fault. In particular, the ECM72 may indicate that the electro-hydraulic control system 60 has failedto increase the main line pressure MP to the second pressure level PL2(i.e. the main line pressure MP has failed low) and/or that theelectro-hydraulic control system 60 may be experiencing excessive fluidleakage.

If the ECM 72 determines that the pressure switch changed states at thesecond diagnostic point DP2, then the ECM 72 may proceeds with normaloperation of the electro-hydraulic control system 60 at block 548. Atblock 550, the ECM 72 may generate regulator control signals thatrequest the main regulator valve 66 to reduce the main line pressure MPto a third pressure level PL3 in anticipation of turning the vehicleoff, in response to a request to turn the engine off, and/or in responseto another event. For example, the ECM 72 may request the main regulatorvalve 66 to reduce the main line pressure MP to the third pressure levelPL3 in response to a user placing the vehicle in a parked state and/orturning an ignition key to an off state.

In one embodiment, the ECM 72 generates regulator control signals thatrequest the main regulator valve 66 to reduce the main line pressure MPto a third pressure level PL3 (e.g. 50 psi) that is less than thethreshold pressure level TH and that is sufficient to fill theelectro-hydraulic control system 60 with fluid. In some embodiments, thethird pressure level PL3 requested by the ECM 72 is the same as thesecond pressure level PL2; however, the third pressure level PL3 maydiffer from the second pressure level PL2 in other embodiments.

As explained above in regard to the second pressure level PL2, the valvewith the pressure switch should transition from a regulating state to anon-regulating state in response to the main line pressure MP beingdecreased to the third pressure level PL3. Moreover, the pressure switchshould transition from an inactive state (e.g. closed) to an activestate (e.g. open) in response to the valve transitioning to thenon-regulating state. Accordingly, the ECM 72 at block 555 determineswhether the pressure switch changed states at a third diagnostic pointDP3. In particular, the ECM 72 in one embodiment at block 555 determinesbased upon the status signal of the pressure switch whether the pressureswitch transitioned from an inactive state (e.g. closed) to an activestate (e.g. open). If the ECM 72 determines that the pressure switch didnot change state at the third diagnostic point DP3, then the ECM 72detects a fault in the electro-hydraulic control system 60 at block 560and may provide signals and/or other indicators of such detected fault.In particular, the ECM 72 may indicate that the electro-hydrauliccontrol system 60 has failed to reduce the main line pressure MP to thethird pressure level PL3 (i.e. the main line pressure MP has failedhigh).

If the ECM 72 determines that the pressure switch changed states at thethird diagnostic point DP3, then the ECM 72 and/or another controller ofthe vehicle may cause the fluid supply system 80 to cease deliver offluid to the electro-hydraulic control system 60. In particular, the ECM72 and/or another controller of the vehicle may generate signals thatcause the engine 20 to turn off. As mentioned above, the pump 84 isengine driven. Accordingly, the fluid supply system 60 ceases to supplyfluid to the electro-hydraulic control system 60 in response to theengine 20 being turned off. Thus, the main line pressure MP is furtherreduced from the third pressure level PL3 to a zero (or substantiallyzero) pressure level. At the zero pressure level, the pressure switch(e.g. 350, 450) should return to an inactive state since the controlmain pressure CP delivered via the control lines 76 is substantiallyreduced.

Accordingly, the ECM 72 at block 565 determines whether the pressureswitch changed states at a fourth diagnostic point DP4. In particular,the ECM 72 in one embodiment at block 565 determines based upon thestatus signal of the pressure switch whether the pressure switchtransitioned from an active state (e.g. open) to an inactive state (e.g.closed). If the ECM 72 determines that the pressure switch did notchange state at the fourth diagnostic point DP4, then the ECM 72 detectsa fault in the electro-hydraulic control system 60 at block 570 and mayprovide signals and/or other indicators of such detected fault. Inparticular, the ECM 72 may indicate that the pressure switch of theelectro-hydraulic control system 60 has failed to an active state (e.g.failed open). Conversely, if the ECM 72 determines that the pressureswitch of the electro-hydraulic control system 60 has changed state atthe fourth diagnostic point DP4, the ECM 72 may indicate that thepressure switch appears to be operating normally at block 575.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as merely illustrative and not restrictive incharacter, it being understood that only illustrative embodiments havebeen shown and described and that all changes and modifications thatcome within the spirit of the disclosure are desired to be protected.

1. A method for detecting faults in an electro-hydraulic control systemfor a transmission, comprising initiating a delivery of fluid to theelectro-hydraulic control system, adjusting regulator control signalsthat request a main regulator valve of the electro-hydraulic controlsystem to develop a main line pressure, wherein adjusting regulatorcontrol signals comprises generating regulator control signals thatrequest the main regulator valve to increase the main line pressure froma nominal level to a first pressure level and regulator control signalsthat request the main regulator valve to increase the main line pressurefrom the first pressure level to a second pressure level, receivingstatus signals that indicate status of a pressure switch of theelectro-hydraulic control system, status of the pressure switch beingbased upon the main line pressure, detecting faults based upon regulatorcontrol signals requesting the main line pressure to increase to thefirst pressure level or the second pressure level and status signalsindicative of status of the pressure switch at the corresponding firstpressure level or second pressure level, and generating one or morediagnostic signals that are indicative of detected faults.
 2. The methodof claim 1, further comprising detecting a fault of the pressure switchin response to the status signals indicating the pressure switch is inan active state prior to initiating the delivery of fluid.
 3. The methodof claim 1, further comprising ceasing the delivery of fluid to theelectro-hydraulic control system, and detecting a fault of the pressureswitch in response to the status signals indicating the pressure switchis in an active state after ceasing the delivery of fluid.
 4. The methodof claim 1, wherein detecting faults comprises detecting a fault of theelectro-hydraulic control system in response to status signalsindicating the pressure switch is in an inactive state and regulatorcontrol signals requested the main regulator valve to increase the mainline pressure to the first pressure level.
 5. The method of claim 4,wherein detecting faults further comprises detecting a fault of theelectro-hydraulic control system in response to status signalsindicating the pressure switch is in an active state and regulatorcontrol signals requested the main regulator valve to increase the mainline pressure to the second pressure level.
 6. The method of claim 5,wherein adjusting regulator control signals comprises generatingregulator control signals that request the main regulator valve toreduce the main line pressure from the second pressure level to a thirdpressure level, and detecting faults comprises detecting a fault of theelectro-hydraulic control system in response to status signalsindicating the pressure switch is in an inactive state and regulatorcontrol signals requested the main regulator valve to decrease the mainline pressure to the third pressure level.
 7. The method of claim 1,wherein detecting faults includes detecting, based upon the regulatorcontrol signals and the status signals that indicate status of thepressure switch, that the pressure switch has failed to an open state,and generating one or more diagnostic signals includes generating one ormore diagnostic signals that indicate the pressure switch has failed tothe open state.
 8. The method of claim 1, wherein detecting faultsincludes detecting, based upon the regulator control signals and thestatus signals that indicate status of the pressure switch, that thepressure switch has failed to a closed state, and generating one or morediagnostic signals includes generating one or more diagnostic signalsthat indicate the pressure switch failed to the closed state.
 9. Themethod of claim 1, wherein detecting faults includes detecting, basedupon the regulator control signals and the status signals that indicatestatus of the pressure switch, that a fluid supply source failed todeliver fluid to the electro-hydraulic control system, and generatingone or more diagnostic signals includes generating one or morediagnostic signals that indicate the fluid supply source failed todeliver fluid to the electro-hydraulic control system.
 10. The method ofclaim 1, wherein detecting faults includes detecting, based upon theregulator control signals and the status signals that indicate status ofthe pressure switch, that the electro-hydraulic control system failed toincrease the main line pressure above a threshold pressure levelassociated with the pressure switch, and generating one or morediagnostic signals includes generating one or more diagnostic signalsthat indicate the electro-hydraulic control system failed to increasethe main line pressure above the threshold pressure level.
 11. Themethod of claim 1, wherein detecting faults includes detecting fluidleakage based upon the regulator control signals and the status signalsthat indicate status of the pressure switch, and generating one or morediagnostic signals includes generating one or more diagnostic signalsthat indicate fluid leakage detected.
 12. A method for detecting faultsin an electro-hydraulic control system for a transmission, the methodcomprising: adjusting a main line pressure of the electro-hydrauliccontrol system to a plurality of different pressure levels by (i)increasing the main line pressure to a first pressure level, (ii)increasing the main line pressure from the first pressure level to asecond pressure level, and (iii) decreasing the main line pressure fromthe second pressure level to a third pressure level; receiving a statussignal indicative of a status of a pressure switch of theelectro-hydraulic control system at each of the plurality of differentpressure levels; and detecting a fault as a function of a lack of changein the status of the pressure switch at one of the plurality ofdifferent pressure levels.
 13. The method of claim 12, wherein receivinga status signal comprises: receiving a status signal indicative of thestatus of the pressure switch at the first pressure level, the secondpressure level, and the third pressure level.
 14. The method of claim13, wherein detecting a fault comprises detecting a fault in response tothe status of the pressure switch failing to change from an inactivestate to an active state at the first pressure level.
 15. The method ofclaim 14, wherein detecting a fault comprises detecting a fault inresponse to the status of the pressure switch failing to change from theactive state to the inactive state of the second pressure level.
 16. Themethod of claim 15, wherein detecting a fault comprises detecting afault in response to the status of the pressure switch failing to changefrom the inactive state to the active state of the third pressure level.17. The method of claim 16, further comprising: decreasing the main linepressure from the third pressure level to a fourth pressure level,receiving a status signal indicative of the status of the pressureswitch at the fourth pressure level, and detecting a fault in responseto the status of the pressure switch failing to change from the activestate to the inactive state of the fourth pressure level.